Add support for Chrome policy type that references external data

grit/format/policy_templates/writers/plist_strings_writer.py

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 
 from grit.format.policy_templates.writers import plist_helper
 from grit.format.policy_templates.writers import template_writer
 
 
@@ skipping 31 matching lines @@
     return self.FlattenGroupsAndSortPolicies(policy_list)
 
   def WritePolicy(self, policy):
     '''Add strings to the stringtable corresponding a given policy.
 
     Args:
       policy: The policy for which the strings will be added to the
         string table.
     '''
     desc = policy['desc']
-    if policy['type'] in ('int-enum','string-enum'):
+    if policy['type'] == 'external':
+      # This type can only be set through cloud policy.
+      return
+    elif policy['type'] in ('int-enum','string-enum'):
       # Append the captions of enum items to the description string.
       item_descs = []
       for item in policy['items']:
         item_descs.append(str(item['value']) + ' - ' + item['caption'])
       desc = '\n'.join(item_descs) + '\n' + desc
 
     self._AddToStringTable(policy['name'], policy['label'], desc)
 
   def BeginTemplate(self):
     app_name = plist_helper.GetPlistFriendlyName(self.config['app_name'])
     self._AddToStringTable(
         app_name,
         self.config['app_name'],
         self.messages['mac_chrome_preferences']['text'])
 
   def Init(self):
     # A buffer for the lines of the string table being generated.
     self._out = []
 
   def GetTemplateText(self):
     return '\n'.join(self._out)